The present invention relates to an acidic aqueous composition that is especially useful for removing particulate and metallic contamination from a surface. The present invention is especially useful for removing particulate and metallic contaminants from structures such as those used as interconnect structures in integrated circuit devices such as semiconductor wafers containing copper damascene and dual damascene features. The structures treated according to the present invention include those that have been previously planarized by chemical mechanical polishing.
On VLSI and ULSI semiconductor chips, Al and alloys of Al are used for conventional chip interconnect/wiring material. However, more recently copper and alloys of copper have been a developed as chip interconnect material. The use of copper and copper alloys results in improved device performance when compared to Al and its alloys.
In the fabrication of semiconductor devices, the metallic interconnect material or wiring such as the copper or its alloys is typically planarized after deposition.
Polishing slurries used for this planarization are typically aqueous suspensions comprised of a metal oxide abrasive (such as alumina), organic acids, surfactants, and a suitable oxidizing agent. This process is known as chemical-mechanical polishing (CMP). The oxidizing agent works to enhance mechanical removal of material via a corrosion assisted process. Such oxidizing agents employed in commercially-available or proprietary slurries are typically inorganic metal salts such as FeNO3, or KIO3, and also hydrogen peroxide, present in significant concentrations. Other chemicals added to slurries to improve dispersion or otherwise enhance performance often are organic acids (e.g. citric acid). Sodium, potassium, and iron salts and/or compounds are frequently used in slurry formulations, and significant amounts of these metal ion impurities can remain on the wafer after polishing and post-polish cleaning.
Therefore, a tendency exists for various particulate contaminants to remain on the polished surface. The particulate materials are extremely difficult to remove. This is particularly problematic since the removal must not adversely affect the polished surface.
Furthermore, since the polishing slurries typically contain an oxidizing agent, an oxide layer usually is present on the copper due to oxidization of the copper during the CMP process. This layer may adversely affect the electrical characteristics of the device, and is preferably removed. In fact, this layer may also contribute to the contamination.
Accordingly, a need exists for a post chemical mechanical polishing cleaning chemistry that removes metallic and particulate contamination. In addition, it is desired that the cleaning step remove any residual copper oxides and/or other non-desirable surface films, leaving a bare copper surface.
The problems of developing such a cleaning is further exacerbated by the need to minimize etching of the copper as well as avoiding increased surface roughness to any significant extent.
Moreover, compositions containing fluorides have been suggested. However, it has become desirable to provide fluoride-free compositions due to environmental considerations.
The present invention relates to an acidic aqueous solution that is especially for cleaning metallic/metal ion contaminants and especially metal and non-metal oxide particles remaining at or in the surface of a semiconductor wafer following CMP.
The present invention is particularly useful for removing particulate contaminants from copper. The present invention also removes any residual oxide layer found on the copper surface without etching or increasing the surface roughness of the copper to any significant extent.
In particular, the present invention relates to a fluoride-free aqueous composition comprising about 0.005 to about 16% by weight of at least one dicarboxylic acid, salt thereof or mixture thereof,
about 0.003 to about 4% by weight of at least one hydroxy carboxylic acid, salt thereof or mixture thereof; or an amine group-containing acid and the remainder being substantially water, and
having a pH of about 1 to about 4.
A further aspect of the present invention is concerned with a process for removing particulate contaminants from a copper surface after CMP planarization. In particular, the process comprises contacting a copper surface that has been planarized by CMP with one of the above-disclosed aqueous compositions.
A still further aspect of the present invention relates to a process for fabricating semiconductor integrated circuits. The process comprises forming circuits on the surface of a semiconductor wafer by photolithographic process wherein the circuits comprise copper or copper alloy; planarizing the surface by chemical mechanical polishing; and removing particulate and metallic (e.g.xe2x80x94metal ion) contaminants from the surface by contacting with one of the above-disclosed aqueous compositions.
Still other objects and advantages of the present invention will become readily apparent by those skilled in the art from the following detailed description, wherein it is shown and described only the preferred embodiments of the invention, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, without departing from the invention. Accordingly, the description is to be regarded as illustrative in nature and not as restrictive.
A number of criteria must be considered to establish an acceptable wafer cleaning process. In particular, the ideal cleaning process should reduce particulate and metallic contaminants on the wafer to the level present before the polishing step. Also, the cleaning process and chemistry must be compatible with the materials exposed on the wafer surface after CMP. Furthermore, one should be able to perform the cleaning process safely using commercially available wafer or fabrication equipment. Moreover, it is desirable that the process be relatively inexpensive to implement. Furthermore, environmental considerations make it desirable that the composition be fluoride-free.
The structures treated pursuant to the present invention are typically semiconductor devices having copper interconnects (lines, plugs, vias, global and local interconnects) imbedded into a low k dielectric material such as silicon dioxide, which may also include a capping layer, such as silicon nitride as in low k dielectric/damascene and dual damascene structures. The silicon dioxide is typically a high density plasma deposited silicon dioxide or TEOS (tetraethylorthosilicate).
The copper interconnects typically use either tantalum, tantalum nitride, or titanium or titanium nitride as a barrier or liner material between the copper and the dielectric. As such, the post-CMP cleaning solution is meant to clean up to four or more different materials, copper, the liner material, the dielectric or capping layer, as well as the wafer backside, which is generally a thin layer of oxidized silicon. All these types of materials are exposed on the surface of the semiconductor device during post-CMP cleaning. Accordingly, the cleaning composition must not adversely effect any of these materials to an undesired degree while still effectively removing the contaminants. This places considerable constraints upon developing a suitable composition.
The copper is planarized after deposition by chemical mechanical polishing typically employing an aqueous slurry comprising an abrasive and an oxidizing agent. Such compositions are well known and need not be described in any detail herein. Examples of some chemical mechanical polishing slurries can be found in U.S. Pat. No. 5,527,423 and U.S. Pat. No. 5,693,239, and PCT publication WO 97/43087, disclosures of which are incorporated herein by reference.
The structure is then contacted with a fluoride-free aqueous composition according to the present invention. The composition comprises at least one dicarboxylic acid and/or salt thereof; and at least one hydroxycarboxylic acid and/or salt thereof; or an amine group containing acid.
Use of the term xe2x80x9cfluoride-freexe2x80x9d herein refers to at least substantially fluoride-free (e.g. containing no more than about 100 ppb of fluoride). Typical dicarboxylic acids include those having two to six carbon atoms, and include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid and fumaric acid. The preferred acid is malonic acid. Suitable salts include the alkali metal, alkaline earth metal and ammonium salts. Preferably, a mixture comprising malonic acid and oxalic acid is employed.
Examples of hydroxycarboxylic acids includes malic acid, tartaric acid and citric acid.
The preferred hydroxycarboxylic acid is citric acid. Suitable salts include alkali metal, alkaline earth metal and ammonium salts.
A preferred derivative is ammonium citrate.
The amine-containing acid is preferably glycine.
In addition to water, preferably deionized water, the composition can include minor amounts (e.g. up to about 0.002% by weight of the active portion) of a biocide. A typical biocide is Kathan. Kathan comprises:
1.2% 5-chloro-2-methyl-4-isothiazolin-3-one
0.4% 2-methyl-4-isothiazolin-3-one
1.1% MgCl2 
1.75% Mg(NO3)2 
0.16% copper nitrate trihydrate
water 95.85%.
The dicarboxylic acid and/or salt is typically present in amounts of about 0.005 to about 16 weight %, more typically about 0.1 to about 3 weight % and preferably about 0.3 to about 0.5 weight %. When the preferred mixture of oxalic acid and malonic acid is used, each one is typically present in amounts of about 0.003 to about 8 weight %, more typically about 0.05 to about 1.5 weight % and preferably about 0.1 to about 0.3 weight %.
The hydroxycarboxylic acid is typically present in the composition at amounts of about 0.003% to about 8% by weight, more typically about 0.05 to about 1.5 weight % and preferably about 0.1% to about 0.3% by weight.
When employed, the amino-group containing acid such as glycine is typically employed in amounts of about 0.003 to about 4% by weight, more typically about 0.005 to about 1.5 weight % and preferably about 0.005 to about 0.05% by weight.
In addition, the compositions of the present invention have a pH of about 1 to about 4 and preferably about 1 to about 3, a particular example being about 2. The pH is typically measured using pH paper or suitable pH reference electrode. It has been discovered according to the present invention that the pH is important in achieving objectives of the present invention. In particular, the compositions are capable of removing metallic and non-metallic particulate oxides, as well as silicon dioxide; metal ion contaminants such as K, Ca, Ti, Cr, Mn, Fe, Ni, Cu and Zn; various sulfur and chloride impurities adsorbed on the various surface materials present on the wafer. CuO is thermodynamically unstable within the pH range of the compositions of the present invention.
A further feature of the present invention is that the composition even in concentrated form is relatively stable. For instance, concentrates of the composition comprising about 0.1 to about 16% by weight and preferably about 6% to about 10% by weight of the dicarboxylic acid, about 0.05% to about 8% by weight, and preferably about 3% to about 5% by weight of the dihydroxy carboxylic acid or amino acid and the remainder being substantialy water can be provided and transported to the end user, the user can then dilute it such as about a 19:1 dilution by weight at the process tool for convenience and for economical reasons.
The composition can be used in a double sided brush scrubber to clean whole wafers following a copper CMP polishing step. Moreover, such can be used in a megasonic bath or spray tool cleaning apparatus, or combination thereof.